Comparative Evaluation of Micro Tensile Bond Strength and Microleakage of Ionoseal Glass-Composite as a Fissure Sealant Material, Following Four Different Enamel Surface Pretreatments

Statement of the Problem: Sealants are employed to prevent carious lesion initiation and to arrest caries progression by providing a physical barrier that inhibits accumulation of microorganisms and food particles in pits and fissures. The two most common materials used for sealing pits and fissures are resins and glass-ionomers. Ionoseal from VOCO company is one of the light curing glass-ionomer composite cements, whose mechanical properties should be investigated. Purpose: The aim of this study was to compare the micro tensile bond strength and micro leakage of Ionoseal with different surface pretreatments. Materials and Method: This in vitro experimental study was conducted on five groups of 95 sound human premolars. Each group consisted of five teeth for the micro tensile test and 14 teeth for the micro leakage test. The groups regarding the materials and the methods used were defined as Group 1: 35% phosphoric acid + total etch adhesive + Ionoseal, Group 2: universal adhesive+Ionoseal, Group 3: 35% phosphoric acid + Ionoseal,Group 4: Ionoseal, and Group 5 (control group): 35% phosphoric acid+Embrace fissure sealant. On the pre-pared buccal enamel of each tooth, a 5 mm block of the sealing material was created and thermo cycled. The specimens were serial sectioned to a cross section of about 1×1mm and loaded in a tensile pressure (0.5 mm/min) until failure occurred. For the micro leakage test, the sealing material was placed into the prepared occlusal fissures and teeth were thermo cycled, and then immersed in 5%methylene blue. A section was made buccolingually; the dye penetration rate was measured based on Williams and Winter criteria under a stereomi-croscope. Data was analyzed with one-way ANOVA test and Kruskal-Wallis test. Results: Mean micro tensile bond strength was significantly different between the groups (p< 0.001), and was significantly higher in Group 1. There was no significant difference between the frequency of modes of failure (p= 0.81). The rate of micro leakage was significantly different between the five groups (p< 0.001) and in Group 1 and 3; it was significantly lower than the other three groups. Conclusion: Ionoseal can be used successfully as a fissure sealant material. Etching the enamel surface with phosphoric acid is necessary and the use of a bonding agent before Ionoseal placement improves results.


Introduction
In recent decades, significant advances in caries preven-tion have been made due to a number of factors, including fluoride intake, improved responsiveness to the ben-efits of early care, increased admissions to dental care, more financial coverage by insurance companies, and government-sponsored programs to prevent and repair restorative teeth for children [1]. Regardless of these efforts, dental caries is yet considered as the most common chronic childhood disease [1]. Approximately 56% of children aged 6 to 8 years old have caries in the deciduous teeth and 21% of children aged 6 to 11 years have experienced caries in permanent teeth [1].
Sealants are used to prevent the onset or to stop the progression of caries with the aim of providing a physical barrier that prevents the accumulation of food particles and microorganisms in the pits and fissures [2].
Children and adolescents receiving sealants on healthy occlusal surfaces or carious lesions without pit cavities and fissures in deciduous and permanent molars showed a 76% reduction in the risk of new caries within two years of follow-up compared to control groups [1]. Even after seven years or more of follow-up, children and adolescents with sealants showed a 29% incidence of caries compared to 74% incidence of caries in the nonsealant group [1].
The most common materials used to seal pits and fissures are resins and glass ionomers. It has been shown that both of these materials have the potential to prevent caries [3]. In 1970, Bonocore introduced the resin Bisphenol-a-glycidyl methacrylate, known as BIS-GMA [4]. It was used as a base for many sealants and composites due to its resistance to bacterial decomposition and the formation of a durable bond with etched enamel. In 1974, glass ionomer cements (GICs) were introduced by Mclean and Wilson to seal dental grooves [4]. Resin-modified glass ionomers (RMGICs) were introduced with the attempt of overcoming problems such as moisture sensitivity and weak physical properties of conventional glass ionomers. RMGIC enhanced the physical properties of conventional glass ionomers while preserving clinical benefits like adhesion and fluoride release and providing some protection against caries [5].
VOCO has introduced Ionoseal (Ionoseal, VOCO GmbH, Cuxhaven, Germany) as a light-curing glass ionomer composite [6]. Ionoseal has been shown to be highly moisturizing, making it more convenient to use in hard-to-reach areas. This material is highly favorable for the dentist to use and, as claimed by the manufactur-er, has great mechanical properties, high compressive strength, and biocompatibility of the product is sustained by the concurrent release of fluoride. Moreover, this material can be cured by light in a few seconds; therefore, its application is effectively time-saving [6].
It has been shown that the microleakage of this material is equal to or even less than the conventional materials used for fissure sealants. It has also been indicated that regarding the high amount of micro hardness of Ionoseal, its ease of use, and timesaving benefits, it is a good option as a reliable restorative material for dental care in children [6]. Ionoseal can be applied on enamel without surface preparation with phosphoric acid as recommended by the manufacturer. Ease of use of this material and elimination of etching and rinsing steps in the pediatric dentistry is very important. Especially in noncooperative children, and due to the importance of isolation in the success of fissure sealant, rapid clinical application of a sealant is very important. Thus, this material could provide reduced working time and greater success as well as greater parent satisfaction [6].
McMurphy et al. [2] showed that adding bonding material without curing before sealant therapy reduces the micro tensile bond strength and the exposure to the thermo cycling had no effect on the micro tensile bond strength. In a study by Nahvi et al. [7], it was shown that the use of bonding significantly reduced the micro leakage of fissure sealants.
Due to the lack of sufficient studies on the application of Ionoseal as a fissure sealant and because of its excellent advantages, such as ease of use, faster work process, and suitable physical and mechanical properties, this study was designed to evaluate the micro leakage and micro tensile bond strength of Ionoseal in four different surface preparations.

Materials and Method
The present laboratory experimental study was registered with the Ethics index IR.IAU.KHUISF.REC.1398.
122. In this study, 95 human premolars, extracted for orthodontic purposes, which had no structural defects, cracks, or fractures and were collected. For disinfection, the teeth were brushed and then immersed in chloramine 0.5% T solution for one week [8]. After keeping the teeth in distilled water at room temperature, the study groups were determined in the following order:  Table 1.

Preparation of samples for micro tensile bond strength
Twenty-five teeth were selected and their roots were removed from the CEJ area by a non-stop cutting machine and then randomly divided into five groups. Each of the four experimental groups consisted of five teeth with surface preparation before applying Ionoseal according to the manufacturer's instructions, and the control group consisted of five teeth (n=5) in which surface preparation was done and conventional fissure sealant was applied.
In Group 1, the enamel of the buccal surface of the five teeth was etched with 35% phosphoric acid for 20 seconds, then rinsed with a water spray for 10 seconds, and dried with air spray for five seconds. Solobond M adhesive, a fifth-generation bonding system, was then applied to the etched enamel. According to the manufacturer's instructions, after 30 seconds of adhesive application, it was sprayed with air and then cured for 20 seconds by a LED light curing device.
In Group 2, on the enamel of the buccal surface of the five samples, the Universal Adhesive (Futurabond U) was applied according to the manufacturer's instructions without the use of acid etching. The adhesive was applied to the enamel by a micro brush for 20 seconds, then sprayed with air for five seconds, and cured for 10 seconds.
In Group 3, the enamel of the buccal surfaces of the five teeth were etched with 35% phosphoric acid for 20 seconds, then rinsed with water spray for 10 seconds, and dried with air spray for five seconds.
In Group 4, no preparation was performed on the buccal enamel surface of the samples. Ionoseal was applied   Table 2. An observer categorized the color penetration while blinded to the types of sample [8].
Data were analyzed using one-way ANOVA test and Kruskal-Wallis test and SPSS25 software.

Results
Due to the adhesive failure of all samples in the fourth Dye penetration into less than one third of the entire length of the surface between the sealant and the tooth structure Grade 2 Dye penetration into one third to two thirds of the entire length of the surface between the sealant and the tooth structure Grade 3 Dye penetration into more than two thirds of the entire length of the surface between the sealant and the tooth structure group, this group did not enter the micro tensile bond strength test. Kolmogorov-Smirnov test showed that the bond strength in all groups followed the normal distribution. Therefore, one-way analysis of variance was used to compare bond strength between the four groups.
The one-way analysis of variance test showed that the mean bond strength was significantly different between the four groups (p< 0.001). The Tukey post hoc test showed that the average bond strength in the first group was significantly higher than the second two groups (p< 0.001), third (p= 0.02) and fifth (p< 0.001).
The mean bond strength in the third group was significantly higher than the second group (p= 0.004), but there was no significant difference between the fifth group and the second two groups (p= 0.10) and the third (p= 0.19). The average bond strength is shown in Table   3. The chi-square test with a likelihood ratio showed that the frequency distribution of the fracture type was not significantly different between the four groups (p= 0.81) ( Table 4). The Kruskal-Wallis test showed that the amount of microleakage was significantly different between the five groups (p< 0.001) ( Table 5). The Mann-Whitney test showed that the amount of microleakage in groups 1 and 3 was significantly lower than the other three groups. There was no significant difference between the two groups 1 and 3 and between the three groups 2, 4 and 5 (Table 6).

Discussion
The long-term clinical success of fissure sealants is strongly interrelated to their proper employment. A dry surface of enamel is essential to achieve proper adhesion [9]. Therefore, the use of materials with less sensitivity to moisture and easier application techniques is very important, especially in difficult isolated conditions [9].
VOCO has introduced Ionoseal as a glass ionomer composite cement with high compressive strength and biocompatibility that can be used quickly (cured by light in a few seconds) as a suitable material for fissure sealants [6]. Moreover, Ionoseal can be applied on tooth enamel without surface preparation as recommended by the manufacturer. According to the advantages of Ionoseal, in this study, the physical properties of this material have been investigated using two different application methods (micro tensile bond strength and microleakage).
The clinical success of dental sealants is associated with their ability to adhere firmly to the enamel surface and to separate pits and fissures from the oral environment safely [10]. In the present study, the micro tensile bond strength was measured for the first, second, third, and fifth groups. In the fourth group (using Ionoseal without surface preparation on enamel); all samples failed as adhesive type during the preparation process. It seems that the strength of Ionoseal bond on enamel without surface preparation is not enough to withstand the stress of the sample preparation process (slices with a cross section of 1×1 mm). The highest bond strength was seen in the first group (total etch adhesive and Ionoseal) and was significantly higher than the other groups. The results are in line with the findings of many studies, including that of Papacchini et al. [10], Pouyanfar et al. [8], and Autio-Gold et al. [12], in which the use of a total etched adhesive between fissure sealant and etched enamel was suggested to increase adhesion and compatibility. However, in some studies such as the study of Murphy et al. [2] as well as the study of Bagheri et al. [13], the use of adhesives before sealant application did not significantly improve bond strength.
Also, the average bond strength of the third group (etch and Ionoseal) was significantly higher than the second group (self-etch and Ionoseal). In fact, the low-  [7] showed that the use of bonding agent along with the usual method of fissure sealant significantly reduced microleakage. In addition, the use of self-etch bonding agent was reported to be less effective in reducing microleakage compared to using the acid etching method with the bonding agent [7]. In the present study, the use of universal self-etch bond with Ionoseal showed the weakest results in bond strength and microleakage, which is in line with the results of the study of Hannig et al. [15] .However, in the study of Nahvi et al. [7], regardless of the type of adhesive system, the amount of microleakage was reduced by adding a bonding agent, which is different from the present study. In the study of Morales et al. [18], the use of bonding agent with acid etch significantly reduced the microleakage of fissure sealants compared to the usual method or the self-etch adhesive (in accordance with the present study), but the self-etch adhesive and the con-